Frequency-dependent selection at the amylase locus in Drosophila melanogaster

View/Open

Date

Author

Metadata

Abstract

A. strain of Drosophila melanog-aster deficient in
null
amylase activity (Amylase ) was isolated from a wild
null
population of flies. The survivorship of Amylase
homozygous flies is very low when the principal dietary
carbohydrate source is starch. However, the survivorship of the
null
Amylase genotype is comparable to the wild type when the
dietary starch is replaced by glucose. In addition, the
null
viability of the amylase-producing and Amylase strains is
comparable v and very lm<] f on a medium with no carbohydrates .
Furthermore, amylase-producing genotypes were shovm to
excrete enzymatically active amylase protein into the food
medium. The excreted amylase causes the external breakdown of
dietary starch to sugar. These results led to the following
null
prediction: the viability of the A.mvlase genotype (fed on a
starch rich diet) might increase in the presence of individuals
which were amylase-producing. It was shown experimentally that
such an increase in viability did in fact occur and that this increase
v\Tas proportional to the number of mnylase..::producing fli.es present.
These results provide a unique example of a non-"competi ti ve
inter-genotype interaction, and one where the underlying physio~
logical and biochemical mechanism has been fully understood.